The present invention is related to polarization viewers. More specifically, the present invention is related to a polarization viewer that preferably forms a transmitted radiance sinusoid in order to form an image based on polarization information concerning a scene.
In the context of physics-based vision there is in fact a compelling motivation to study polarization vision-polarization affords a more general description of light than does intensity, and can therefore provide a richer set of descriptive physical constraints for the interpretation of an imaged scene. As intensity is the linear sum of polarization components, intensity images physically represent reduced polarization information. Because the study of polarization vision is more general than intensity vision, there are polarization cues that can immensely simplify some important visual tasks (e.g., region and edge segmentation, material classification, etc. . . ) which are more complicated or possibly infeasible when limited to using intensity and color information. A detailed description of a variety of polarization-based vision methods are contained in L. B. Wolff. Surface orientation from polarization images. In Proceedings of Optics, Illumination and Image Sensing for Machine Vision II, Volume 850, pages 110-121, Cambridge, Mass., November 1987. SPIE; L. B. Wolff. Polarization-based material classification from specular reflection. IEEE Transactions on Pattern Analysis and Machine Intelligence (PAMI), 12(11):1059-1071, November 1990; L. B. Wolff and T. E. Boult. Constraining object features using a polarization reflectance model. IEEE Transactions on Pattern Analysis and Machine Intelligence (PAMI), 13(7):635-657, July 1991; L. B. Wolff. Polarization Methods in Computer Vision. PhD thesis, Columbia University, January 1991; T. E. Boult and L. B. Wolff. Physically-based edge labeling. In Proceedings of IEEE Conference on Computer Vision and Pattern Recognition (CVPR), Maui, June 1991.
A criticism that has sometimes been leveled at polarization-based vision methods is the inconvenience of obtaining polarization component images by having to place a linear polarizing filter in front of an intensity CCD camera and mechanically rotating this filter by hand or by motor into different orientations. This inconvenience is a result of commercially available camera sensors being geared towards taking intensity images instead of polarization images. There are considerable advantages to building a camera sensor geared towards doing polarization vision, capable of taking polarization images without external mechanical manipulation of a filter. There already exist polarization-based vision methods that can significantly benefit a number of application areas such as aerial reconnaissance, autonomous navigation, inspection, and, manufacturing and quality control. A polarization camera would make polarization-based vision methods more accessible to these application areas and others. It should be fully realized that as intensity is a compression of polarization component information, a polarization camera can function as a conventional intensity camera, so that intensity vision methods can be implemented by such a camera either alone, or, together with polarization-based vision methods. As intensity-based methods are physical instances of polarization-based methods, a camera sensor geared towards polarization-vision does not in any way exclude intensity vision, it only generalizes it providing more physical input to an automated vision system. Adding color sensing capability to a polarization camera makes it possible to sense the complete set of electromagnetic parameters of light incident on the camera.
The present invention in a preferred embodiment involves a polarization viewer that does not require any external mechanical manipulation of a filter to form a transmitted radiance sinusoid. With the sinusoid, polarization states can be mapped into hue, saturation and intensity which is a very convenient representation for a polarization image.
The present invention pertains to a polarization viewer. The polarization viewer comprises a mechanism or means for forming a broadview image having a spectral width preferably greater than 2 angstroms and 0.50xc2x0 based on polarization information of a scene, although it can be used in that range. The polarization viewer is also comprised of a mechanism or means for providing polarization information to the forming mechanism or means. The providing mechanism or means is in communication with the forming mechanism or means.
In a first embodiment, the providing mechanism or means includes a camera mechanism or means in communication with the forming mechanism or means. The camera mechanism or means includes a fixed polarizer analyzer disposed such that electromagnetic radiation entering the camera mechanism or means passes through the polarizer analyzer. The providing mechanism or means can also include a mechanism or means for steering a polarization plane of the radiation. The steering mechanism or means is disposed such that radiation passing through the polarizer analyzer first passes through the steering mechanism or means. The steering mechanism or means preferably includes a first twist crystal in a first embodiment and at least a second twist crystal aligned with the first twist crystal such that radiation passing through the first crystal then passes through the second crystal in a second embodiment. Each crystal has a first state and a second state. The first state does not effect the polarization plane of the radiation as the radiation passes through the crystal. The second state rotates the polarization plane of the radiation as the radiation passes through the crystal.
In another embodiment, the providing mechanism or means includes a CCD chip having a plurality of pixels which forms a signal from electromagnetic radiation received at the pixels. The providing mechanism or means also includes a mechanism or means for allowing radiation of a predetermined polarization to pass through each pixel. The allowing mechanism or means is disposed over the chip such that the radiation passes through the allowing mechanism or means before it is received by the chip.
In yet another embodiment, the providing mechanism or means includes a first CCD chip which produces a first signal based on electromagnetic radiation it receives. The providing mechanism or means also includes a first beam-splitter disposed such that radiation reflected by the first beamsplitter is received by the first CCD chip. There is additionally a second CCD chip which produces a second signal based on electromagnetic radiation it receives which is transmitted by the first beamsplitter. The second CCD chip is disposed such that it receives radiation transmitted by the first beamsplitter Moreover, the providing mechanism or means preferably can include a mechanism or means for creating polarization information corresponding to a different polarization orientation than that corresponding with the first or second CCD chip by themselves.
The present invention also pertains to a viewer for forming an image of a scene. The viewer is comprised of a mechanism or means for forming a transmitted radiance sinusoid based on polarization information of a scene and producing the image based on the sinusoid. The viewer is also comprised of a mechanism or means for providing polarization information to the forming mechanism or means. The providing mechanism or means is in communication with the forming mechanism or means.
The present invention additionally pertains to a polarization viewer. The polarization viewer is comprised of a mechanism or means for obtaining polarization information about a scene. The obtaining mechanism or means has no moving mechanical parts. The present invention also pertains to a mechanism or means for forming an image from the polarization information. The forming mechanism or means is in communication with the obtaining mechanism or means.
The present invention also pertains to a viewer that can form a color image with respect to polarization.